HAPPY CAMP, Calif. (AP) â€” Two wildfires sparked by lightning nearly three weeks ago were still growing on Saturday while threatening as many as 250 homes in far Northern California.

Low humidity and warm weather helped the fires burning in the Klamath National Forest one mile east of the gold mining and logging town of Happy Camp continue its sweep through steep terrain packed with trees desiccated by the state’s extreme drought, Forest Service spokesman Marc Peebles said.

The two fires are the largest among about 20 that broke out in the forest when a thunderstorm moved through the area on Aug. 11. Originally located a few miles apart, they had merged by Saturday morning and together charred more than 90 square miles, about 21 square miles more than a day earlier.

“These trees are very stressed. They are very dry. Firefighters are seeing burning conditions like they have never seen before or for many years,” Peebles said.

The threatened homes, which were put an under mandatory evacuation orders on Friday, include cabins and other public structures within the forest and private houses in Siskiyou County, he said.

Nearly 2,000 firefighters and 11 helicopters are assigned to the Happy Camp Complex blazes. As of Saturday, they remained just 15 percent contained.

Cloudy skies, cooler temperatures and lighter winds helped slow the fire on the western flank of the fire, the U.S. Forest Service said. However, the shifting winds forecast for Sunday could increase fire activity on the southern flank.

Meanwhile, another series of fires burning in the Klamath National Forest about 69 miles south of Happy Camp that started with lightning strikes on July 31 remained 73 percent contained.